1. Field of the Invention
The present invention relates to a portable, combustion-engined tool, in particular, a setting tool including a collapsible combustion chamber divided by a separation plate in a forechamber section having an ignition device and at least one further chamber section, with the forechamber section being limited by a movable combustion chamber wall arranged parallel to the separation plate, and with the separation plate having a plurality of openings which communicates the forechamber section with the at least one further chamber section.
2. Description of the Prior Art
A portable, combustion-engined tool described above is disclosed in the German Publication No. 199 50 352.
After the ignition process has been initiated in order to combust a fuel gas mixture, which fills the combustion chamber, the locking of the movable combustion chamber wall is lifted, a spring force provides for movement of the movable wall in a direction toward the piston, which adjoins the combustion chamber, whereby the combustion chamber is freed from waste gases. With this, the separation plate also moves in the direction toward the piston and, after a while, the movable wall lies on the separation plate, with the separation plate lying practically on the piston. As a result, the volume of the combustion chamber becomes practically reduced to zero. During the movement of the movable wall and the separation plate toward the piston, the forechamber section is deaerated only through the openings in the separation plate. To this end, at least one of the through-openings of the separation plate should be aligned with an exhaust valve located opposite the separation plate. If this is not the case, and the movable wall and the separation plate start to move toward each other only after the volume of the main or further chamber section has been reduced to zero, deaeration or the reduction of volume of the forechamber section takes place very slowly. This requires that at least one of the through-openings of the separation is exactly aligned with the opposite exhaust valve in order to insure a more rapid deaeration of the forechamber section. Insuring such an alignment is a very tedious job.
Accordingly, an object of the present invention is to provide means which would insure a rapid deaeration of the forechamber section in a tool of the above-described type under any circumstances.
This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing, in the combustion chamber, collapse control means for controlling the movement of the movable wall and the separation plate, after the combustion of the gas mixture in the combustion chamber, so that the forechamber section collapses first and only then, the further chamber section collapses. When the combustion chamber has only two chamber sections, the further chamber section is called a main chamber section.
With the collapse control means according to the present invention, even if for some reasons, the exhaust valve is not aligned with the associated opening, a complete collapse of the combustion chamber can still be effected as, initially, only the movable wall is displaced toward the separation plate to reduce the volume of the forechamber section With the displacement of the movable wall, the waste gas filling the forechamber section is expelled from the forechamber section through the openings in the separation plate into the further or main chamber section. Only after the volume of the forechamber section has been reduced to zero, the movable wall and the separation plate are displaced together in the direction toward the piston in order to reduce the volume of the main chamber section also to zero. With such controlled displacement, a complete deaeration and/or reduction of the volume of the entire combustion chamber is insured under all circumstances.
The collapse control means can be formed in different ways. Thus, the collapse control means can so preload the movable wall and the separation plate relative to each other that they first would be displaced toward each other and only then would be displaced together in a direction toward the piston. To this end, e.g., the central projection or lug of the separation plate can project through the movable wall, with a compression spring being arranged between the free end of the lug and the movable wall. The spring retains the separation plate in its position at the beginning of movement of the movable wall in a direction toward the piston. As a result, first, the volume of the forechamber section is reduced to zero and it is deaerated before the reduction of volume of the main chamber section begins.
The collapse control means for controlling the movement of the movable wall and the separation plate can also determine the friction between the movable wall and the combustion chamber, on one hand, and between the separation plate and the combustion chamber on the other hand. When, e.g., the movable wall, for reducing the volume of the forechamber section, is driven by outer adjusting means, high friction between the separation plate and the combustion chamber, e.g., can insure that the separation plate remains stationary until the movable wall abuts it. In this way likewise, first, the forechamber section collapses, and the collapse of the main chamber section follows the collapse of the forechamber section.
Further, the collapse control means can be formed as means for a pneumatic control of the movement of the movable wall and the separation plate. In this case, the movement control of the displacement of the movable wall and the separation plate can be programmed.
According to further advantageous embodiment of the present invention, the through-openings of the separation plate can be formed as check valves which provide for gas flow only from the forechamber section into the further or main chamber section.
For obtaining a high piston energy, the combustion, e.g., in the main chamber section, should take place as rapidly as possible. A return flow from the main chamber section into the forechamber section results in an early expansion which, in turn, leads to the cooling down of the flame formed in the main chamber section. The pressure in the main chamber, dependent on the size of the forechamber section, becomes reduced or increases very slowly. In addition, a portion of the fuel gas mixture is forced back into the forechamber section and bums there. This portion of the combustion takes place in a timedelayed manner and contributes little to the piston energy. Providing check valves in the separation plate in collapsible systems permits to increase the energy yield.
Providing check valves in the separation plate insures flow only in one direction, namely, from the forechamber section into the main chamber section. This means narrowing in the flow direction and feeding of the fresh air into the forechamber section. In this case also, the collapse of the chamber sections should be so controlled that the forechamber section collapses first. If this is not the case, and the main chamber section collapses first, the check valves would not be open any more after the collapse, and the deaeration of the forechamber would practically stop.
Further, the movable wall can also be provided with at least one check valve which enables flow only into the forechamber section. Through this check valve, the forechamber section can be filled with fresh air when the movable wall moves away from the separation wall and the chamber sections expand. Upon expansion of the main chamber section, the fresh air enters it through the check valves in the separation plate, with the fresh air thus filling the entire combustion chamber.
The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiments, when read with reference to the accompanying drawings.